if(${RENDERING} MATCHES SFML)
    set(SOURCE ${CMAKE_CURRENT_LIST_DIR}/SFML/Rendering.cpp)
elseif(${RENDERING} MATCHES Metal)
    set(SOURCE ${CMAKE_CURRENT_LIST_DIR}/Metal/Rendering.mm)
elseif(${RENDERING} MATCHES OpenGL)
    set(SOURCE ${CMAKE_CURRENT_LIST_DIR}/OpenGL/Rendering.cpp)
else()
    message(FATAL_ERROR "Rendering interface '${RENDERING}' is not supported.")
endif()

set(SOURCE ${SOURCE} PARENT_SCOPE)
